On the origin and nature of the pituitary gland capsule.

Observations under the operating microscope confirming the presence of a pituitary capsule are reported. This capsule envelops the anterior lobe of the pituitary, the neurohypophysis, and the pituitary stalk. It merges along the stalk with the intracranial pia mater. The origin and nature of this capsule are discussed in light of the known facts of development of the pituitary gland and surrounding structures. It is concluded that the pituitary gland capsule is a derivative of the primitive pia mater.